A method for hydrothermally modifying silicon carbide powder with small molecule organic acid, modified silicon carbide powder, modified silicon carbide slurry and application thereof

Abstract

The present invention provides a method for hydrothermally modifying silicon carbide powder with a small molecule organic acid, modified silicon carbide powder, modified silicon carbide slurry and application, and relates to the technical field of ceramic materials. The method for hydrothermally modifying silicon carbide powder with a small molecule organic acid provided by the present invention comprises the following steps: acid washing the silicon carbide powder to obtain pure silicon carbide powder; mixing the pure silicon carbide powder with an alkali solution and performing an activation treatment to obtain activated silicon carbide powder; mixing the activated silicon carbide powder with a small molecule organic acid and performing a hydrothermal reaction, and washing the obtained powder with a sodium humate solution to obtain modified silicon carbide powder. The modified silicon carbide powder prepared by the present invention can prepare a slurry with a solid content of 50 to 55 vol%, a viscosity of <1 Pa·s, and no obvious sedimentation after standing for more than 48 hours, and the slurry has excellent fluidity, dispersibility and stability, and can meet the requirements of colloidal molding process conditions.

Description

Technical Field

[0001] The invention relates to the technical field of ceramic materials, and in particular to a method for hydrothermally modifying silicon carbide powder using a small molecule organic acid, the modified silicon carbide powder, a modified silicon carbide slurry and applications. Background Art

[0002] Silicon carbide is a commonly used ceramic material with excellent properties such as high strength, high hardness, chemical corrosion resistance, good oxidation resistance, high thermal conductivity and small thermal expansion coefficient. It is widely used as a structural material in high temperature, high power and mechanical fields.

[0003] The molding process is the key technology for preparing silicon carbide ceramics. The molding process affects the number, degree and uniformity of defects in ceramic materials, thereby affecting the uniformity, density and mechanical properties of the microstructure of ceramic materials. Colloidal molding has the advantages of simple and efficient process, high yield, good uniformity, ability to prepare complex-shaped parts and low cost. It is a key technology for the industrialization of high-performance silicon carbide structural ceramics and has received widespread attention. The requirements of the colloidal molding process for ceramic slurry are: high solid content of slurry (solid content ≥50vol%), low viscosity (≤1Pa·s) and good stability.

[0004] The surface modification of silicon carbide powder is mainly carried out by (1) removing impurity ions and increasing the double electric layer on the powder surface; (2) using silane coupling agents or macromolecular organic matter grafting or coating methods to increase the steric hindrance on the powder surface; or using the above methods (1) and (2) in combination. Su Xiaohong et al. (Su Xiaohong, Zhou Bo, Wu Qide, Ji Xiaoli et al. Study on the influence of surface modification of silicon carbide powder on dispersion performance [J]. China Powder Technology, 2007, 5: 27-30.) used salicylic acid and acrylamide to modify silicon carbide powder. Ji Xiaoli et al. (Ji Xiaoli, Zheng Caihua, Wei Lei et al. Study on surface modification of SiC micropowder with aminosilane coupling agent [J]. Chemistry and Bioengineering, 2008, 5 (1): 21-23.) used silane coupling agents to modify the surface of silicon carbide powder. The silicon carbide powder was modified by a polyethylene glycol agent. Guo Xingzhong et al. (Guo Xingzhong, Yang Hui, Wang Jianwu, Cao Ming, etc. Characterization of physical properties of SiC powder surface modified with polyethylene glycol [J]. Materials Engineering, 2004, 3: 7-10.) used polyethylene glycol to modify the silicon carbide powder. Although a slurry with high solid content and low viscosity was obtained, the macromolecular organic matter has the disadvantage of self-aggregation and is prone to self-aggregation in the dispersed phase to form a large number of agglomerates, which in turn reduces the stability of the slurry. Summary of the invention

[0005] The purpose of the present invention is to provide a method for hydrothermally modifying silicon carbide powder with a small molecule organic acid, modified silicon carbide powder, modified silicon carbide slurry and application. The modified silicon carbide powder prepared by the present invention can be used to prepare silicon carbide slurry with high solid content, low viscosity and good stability.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for hydrothermally modifying silicon carbide powder using a small molecule organic acid, comprising the following steps:

[0008] The silicon carbide powder is acid-washed to obtain pure silicon carbide powder;

[0009] The pure silicon carbide powder is mixed with an alkali solution and activated to obtain activated silicon carbide powder;

[0010] The activated silicon carbide powder and a small molecule organic acid are mixed and subjected to a hydrothermal reaction. The obtained powder is washed with a sodium humate solution to obtain a modified silicon carbide powder.

[0011] Preferably, the pickling method comprises: immersing the silicon carbide powder in a hydrochloric acid solution.

[0012] Preferably, the alkali solution comprises sodium hydroxide solution, potassium hydroxide solution or sodium carbonate solution.

[0013] Preferably, the temperature of the activation treatment is 80-120° C.; the time of the activation treatment is 0.5-2 h.

[0014] Preferably, the small molecule organic acid comprises acetic acid, propionic acid, butyric acid or isobutyric acid.

[0015] Preferably, the mass ratio of the activated silicon carbide powder to the small molecule organic acid is 1-2:1-2.

[0016] Preferably, the temperature of the hydrothermal reaction is 80-120° C.; the time of the hydrothermal reaction is 0.5-4.0 h.

[0017] The present invention provides modified silicon carbide powder prepared by the method described in the above technical solution, comprising silicon carbide and an ester modified layer and sodium humate sequentially coated on the surface of the silicon carbide.

[0018] The present invention provides a modified silicon carbide slurry, which is composed of the modified silicon carbide powder described in the above technical solution and water; the solid content of the modified silicon carbide slurry is 50-55 vol%; and the viscosity is less than 1 Pa·s.

[0019] The present invention also provides the use of the modified silicon carbide slurry described in the above technical solution in the preparation of silicon carbide ceramics.

[0020] The present invention provides a method for hydrothermally modifying silicon carbide powder with a small molecule organic acid, comprising the following steps: acid-washing the silicon carbide powder to obtain pure silicon carbide powder; mixing the pure silicon carbide powder with an alkali solution, performing an activation treatment, and obtaining activated silicon carbide powder; mixing the activated silicon carbide powder with a small molecule organic acid, performing a hydrothermal reaction, and washing the obtained powder with a sodium humate solution to obtain modified silicon carbide powder. The present invention removes metal impurity ions (iron, magnesium, calcium, zinc) on the surface of the silicon carbide powder by acid washing; using an alkali solution to remove SiO 2 The layer is activated; the activated silicon carbide powder obtained is then subjected to a hydrothermal reaction with a small molecule organic acid to generate an ester modified layer to obtain a modified silicon carbide powder. The present invention uses a hydrothermal reaction to make the small molecule organic acid and the activated silanol group on the surface of the silicon carbide powder produce a strong bond, and utilizes the dual effects of steric hindrance and electrostatic stabilization effect, thereby improving the Zeta potential of the particle surface, increasing the double electric layer repulsion, reducing the agglomeration between powders, and improving the dispersion stability of the slurry. In the present invention, the sodium humate solution is alkaline and can neutralize excess small molecule organic acid, while the excess sodium humate will be adsorbed on the surface of the modified silicon carbide powder; when the modified silicon carbide powder is added to water and stirred to prepare a slurry, the sodium humate adsorbed on the surface of the powder is dissociated and hydrolyzed, which significantly increases the absolute value of the Zeta potential and the thickness of the double electric layer on the surface of the silicon carbide powder, so that the water coated in the silicon carbide slurry is released to play a dilution role. The present invention utilizes the water-reducing property of sodium humate to further reduce the viscosity of the slurry and improve the rheological property of the slurry. The modified silicon carbide powder prepared by the present invention can prepare a slurry with a solid content of 50-55 vol%, a viscosity of less than 1 Pa·s, and no obvious sedimentation after standing for more than 48 hours, and the slurry has excellent fluidity, dispersibility and stability, and can meet the requirements of colloidal molding process conditions.

[0021] The modified silicon carbide slurry provided by the present invention can be placed for more than 48 hours, which is conducive to storage. During the production process, the processing margin of the slurry is large, which is conducive to improving production efficiency.

[0022] The invention has simple process, short production cycle and low cost and is suitable for mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of slurry sedimentation in the test example. DETAILED DESCRIPTION

[0024] The present invention provides a method for hydrothermally modifying silicon carbide powder using a small molecule organic acid, comprising the following steps:

[0025] The silicon carbide powder is acid-washed to obtain pure silicon carbide powder;

[0026] The pure silicon carbide powder is mixed with an alkali solution and activated to obtain activated silicon carbide powder;

[0027] The activated silicon carbide powder and a small molecule organic acid are mixed and subjected to a hydrothermal reaction. The obtained powder is washed with a sodium humate solution to obtain a modified silicon carbide powder.

[0028] The present invention carries out pickling of silicon carbide powder to obtain pure silicon carbide powder. In the present invention, the reagent used for pickling is preferably a hydrochloric acid solution; the mass fraction of the hydrochloric acid solution is preferably 1.0-10.0%, more preferably 2-8%, and further preferably 4-5%. In the present invention, the mass ratio of the silicon carbide powder and the hydrochloric acid solution is preferably 1:2. In the present invention, the pickling method preferably includes: soaking the silicon carbide powder in a hydrochloric acid solution. In the present invention, the soaking time is preferably 1-4 hours, more preferably 3 hours.

[0029] In the present invention, after the acid washing, the obtained powder is preferably washed with water until it becomes neutral to obtain pure silicon carbide powder.

[0030] After obtaining pure silicon carbide powder, the present invention mixes the pure silicon carbide powder and alkali solution, performs activation treatment, and obtains activated silicon carbide powder. In the present invention, the alkali solution preferably includes sodium hydroxide solution, potassium hydroxide solution or sodium carbonate solution. In the present invention, the mass fraction of the alkali solution is preferably 1.0-10.0%, more preferably 4-5%. In the present invention, the mass ratio of the pure silicon carbide powder and the alkali solution is preferably 1:2.

[0031] In the present invention, the temperature of the activation treatment is preferably 80-120°C, more preferably 100°C; the time of the activation treatment is preferably 0.5-2h, more preferably 1h. In the present invention, the activation treatment is preferably carried out in a hydrothermal environment.

[0032] In the present invention, after the activation treatment, the obtained system is preferably washed with deionized water, and the excess alkali solution is removed by centrifugation; anhydrous ethanol is then added, stirred evenly, and the supernatant is removed by centrifugation to obtain activated silicon carbide powder. In the present invention, the water content of the activated silicon carbide powder is preferably 0 to 0.02 wt%.

[0033] After obtaining the activated silicon carbide powder, the present invention mixes the activated silicon carbide powder with a small molecule organic acid, performs a hydrothermal reaction, and washes the obtained powder with a sodium humate solution to obtain a modified silicon carbide powder. In the present invention, the small molecule organic acid preferably includes acetic acid, propionic acid, butyric acid or isobutyric acid.

[0034] In the present invention, the mass ratio of the activated silicon carbide powder to the small molecule organic acid is preferably 1-2:1-2, and specifically preferably 2:1, 1:1 or 1:2.

[0035] In the present invention, the temperature of the hydrothermal reaction is preferably 80-120°C; the time of the hydrothermal reaction is preferably 0.5-4.0h, more preferably 1-2h. In the present invention, during the hydrothermal reaction, concentrated sulfuric acid is preferably added to promote the reaction. In the present invention, the mass fraction of the concentrated sulfuric acid is preferably 90-98%; the mass of the concentrated sulfuric acid is preferably 0.05-0.1% of the mass of the activated silicon carbide powder. In the present invention, the concentrated sulfuric acid acts as a catalyst, and the addition of concentrated sulfuric acid can promote the rapid reaction.

[0036] In the present invention, the hydrothermal reaction is preferably carried out in a hydrothermal reactor or a microwave hydrothermal synthesizer.

[0037] In the present invention, after the hydrothermal reaction, the obtained material is preferably centrifuged to remove the supernatant, and the obtained powder is washed with a sodium humate solution and centrifuged to obtain a powder; then the powder is dried to obtain a modified silicon carbide powder. In the present invention, the mass fraction of the sodium humate solution is preferably 1.0 to 10.0%, more preferably 4 to 6%. In the present invention, the drying temperature is preferably 80 to 120°C, more preferably 100 to 120°C; the drying time is preferably 2 to 6 hours, more preferably 2 to 4 hours.

[0038] In the present invention, the sodium humate solution is alkaline and can neutralize excess small molecule organic acid, while the excess sodium humate will be adsorbed on the surface of the modified silicon carbide powder; when the modified silicon carbide powder is added to water, stirred, and prepared into a slurry, the sodium humate adsorbed on the surface of the powder undergoes dissociation and hydrolysis, which significantly increases the absolute value of the Zeta potential and the thickness of the double electric layer on the surface of the silicon carbide powder, so that the water encapsulated in the silicon carbide slurry is released to play a dilution role. The present invention utilizes the water-reducing property of sodium humate to further reduce the viscosity of the slurry and improve the rheological properties of the slurry.

[0039] The present invention provides modified silicon carbide powder prepared by the method described in the above technical solution, comprising silicon carbide and an ester modified layer and sodium humate sequentially coated on the surface of the silicon carbide.

[0040] The present invention provides a modified silicon carbide slurry, which is composed of the modified silicon carbide powder described in the above technical solution and water. In the present invention, the water is preferably deionized water.

[0041] In the present invention, the solid content of the modified silicon carbide slurry is 50-55 vol%, preferably 51-54 vol%; the viscosity is <1 Pa·s, preferably 0.540-0.683 Pa·s, and more preferably 0.571-0.646 Pa·s. In the present invention, the modified silicon carbide slurry is preferably left at room temperature for more than 48 hours without sedimentation.

[0042] The present invention also provides the use of the modified silicon carbide slurry described in the above technical solution in the preparation of silicon carbide ceramics. In the present invention, the preparation method is preferably a colloidal molding process.

[0043] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] Example 1

[0045] (1) mixing silicon carbide powder and 2.0wt% dilute hydrochloric acid solution in a mass ratio of 1:2, soaking for 4 hours, centrifuging at high speed, removing the supernatant, washing with water, and obtaining pure silicon carbide powder with surface metal impurity ions removed;

[0046] (2) The pure silicon carbide powder obtained in step (1) was mixed with 1.0 wt% sodium hydroxide solution in a mass ratio of 1:2, and activated in a hydrothermal environment at 100°C for 1 h to remove SiO 2 Layer activation;

[0047] (3) After the activation in step (2) is completed, the mixture is immediately washed with deionized water and the excess sodium hydroxide solution is removed by high-speed centrifugation; then anhydrous ethanol is added, stirred evenly, and the supernatant is removed by centrifugation to obtain activated silicon carbide powder;

[0048] (4) The activated silicon carbide powder and acetic acid in step (3) are stirred evenly in a mass ratio of 2:1, and concentrated sulfuric acid (mass fraction: 98%) is added at 0.05 wt% of the mass of the activated silicon carbide powder, and the mixture is placed in a microwave hydrothermal synthesizer and reacted at 80° C. for 1.0 h to generate an ester modified layer;

[0049] (5) After the reaction in step (4) is completed, the material is centrifuged to remove the supernatant, and the obtained powder is washed with a 1.0 wt% sodium humate solution to remove unreacted acetic acid, and centrifuged to obtain a powder;

[0050] (6) Drying the powder obtained in step (5) to obtain modified silicon carbide powder.

[0051] (7) The modified silicon carbide powder and deionized water were mixed in a mass ratio of 1:0.256 to prepare a modified silicon carbide slurry with a solid content of 55 vol% at a shear rate of 300 s -1 The apparent viscosity is 0.540 Pa·s.

[0052] Example 2

[0053] (1) mixing silicon carbide powder and 4.0wt% dilute hydrochloric acid solution in a mass ratio of 1:2, soaking for 3 hours, centrifuging at high speed, removing the supernatant, washing with water, and obtaining pure silicon carbide powder with surface metal impurity ions removed;

[0054] (2) The pure silicon carbide powder obtained in step (1) was mixed with 1.0wt% potassium hydroxide solution in a mass ratio of 1:2, and activated in a hydrothermal environment at 80°C for 2h to remove SiO 2 Layer activation;

[0055] (3) After the activation in step (2) is completed, the mixture is immediately washed with deionized water and the excess potassium hydroxide solution is removed by high-speed centrifugation; then anhydrous ethanol is added, stirred evenly, and the supernatant is removed by centrifugation to obtain activated silicon carbide powder;

[0056] (4) The activated silicon carbide powder and propionic acid in step (3) are uniformly stirred in a mass ratio of 1:1, placed in a hydrothermal kettle and reacted at 120° C. for 2 h to generate an ester modified layer;

[0057] (5) After the reaction in step (4) is completed, the material is centrifuged to remove the supernatant, and the obtained powder is washed with a 4.0 wt% sodium humate solution to remove unreacted propionic acid, and centrifuged to obtain a powder;

[0058] (6) Drying the powder obtained in step (5) to obtain modified silicon carbide powder.

[0059] (7) The modified silicon carbide powder and deionized water were mixed in a mass ratio of 1:0.266 to prepare a modified silicon carbide slurry with a solid content of 54 vol% at a shear rate of 300 s -1 The apparent viscosity is 0.571 Pa·s.

[0060] Example 3

[0061] (1) mixing silicon carbide powder and 5.0wt% dilute hydrochloric acid solution in a mass ratio of 1:2, soaking for 3 hours, centrifuging at high speed, removing the supernatant, washing with water, and obtaining pure silicon carbide powder with surface metal impurities removed;

[0062] (2) The pure silicon carbide powder obtained in step (1) was mixed with a 5.0 wt% sodium carbonate solution in a mass ratio of 1:2, and activated in a 120°C hydrothermal environment for 1 h to remove SiO 2 Layer activation;

[0063] (3) After the activation in step (2) is completed, the mixture is immediately washed with deionized water and the excess sodium carbonate solution is removed by high-speed centrifugation; then anhydrous ethanol is added, stirred evenly, and the supernatant is removed by centrifugation to obtain activated silicon carbide powder;

[0064] (4) The activated silicon carbide powder and propionic acid in step (3) are uniformly stirred in a mass ratio of 1:2, placed in a microwave hydrothermal synthesizer and reacted at 120° C. for 0.5 h to generate an ester modified layer;

[0065] (5) After the reaction in step (4) is completed, the material is centrifuged to remove the supernatant, and the obtained powder is washed with a 6.0 wt% sodium humate solution to remove unreacted propionic acid, and centrifuged to obtain a powder;

[0066] (6) Drying the powder obtained in step (5) to obtain modified silicon carbide powder.

[0067] (7) The modified silicon carbide powder and deionized water were mixed in a mass ratio of 1:0.217 to prepare a modified silicon carbide slurry with a solid content of 54 vol% at a shear rate of 300 s -1 The apparent viscosity is 0.646 Pa·s.

[0068] Example 4

[0069] (1) mixing silicon carbide powder and 8.0wt% dilute hydrochloric acid solution in a mass ratio of 1:2, soaking for 1 hour, centrifuging at high speed, removing the supernatant, washing with water, and obtaining pure silicon carbide powder with surface metal impurity ions removed;

[0070] (2) The pure silicon carbide powder obtained in step (1) was mixed with 4.0wt% sodium carbonate solution in a mass ratio of 1:2, and activated in a hydrothermal environment at 80°C for 2h to remove SiO 2 Layer activation;

[0071] (3) After the activation in step (2) is completed, the mixture is immediately washed with deionized water and the excess sodium carbonate solution is removed by high-speed centrifugation; then anhydrous ethanol is added, stirred evenly, and the supernatant is removed by centrifugation to obtain activated silicon carbide powder;

[0072] (4) The activated silicon carbide powder and isobutyric acid in step (3) are uniformly stirred in a mass ratio of 1:2, and concentrated sulfuric acid (mass fraction is 90%) with a mass ratio of 0.1wt% of the activated silicon carbide powder is added, and the mixture is placed in a hydrothermal kettle and reacted at 120°C for 2h to generate an ester modified layer;

[0073] (5) After the reaction in step (4) is completed, the material is centrifuged to remove the supernatant, and the obtained powder is washed with a 6.0 wt% sodium humate solution to remove unreacted isobutyric acid, and centrifuged to obtain a powder;

[0074] (6) Drying the powder obtained in step (5) to obtain modified silicon carbide powder.

[0075] (7) The modified silicon carbide powder and deionized water were mixed in a mass ratio of 1:0.236 to prepare a modified silicon carbide slurry with a solid content of 51 vol% at a shear rate of 300 s -1 The apparent viscosity is 0.683 Pa·s.

[0076] Test Case

[0077] The modified silicon carbide powder prepared in Examples 1 to 4 was mixed with deionized water to prepare a 10 vol% modified silicon carbide slurry; the stability of the modified silicon carbide slurry prepared by the present invention was characterized by a sedimentation experiment, as shown in the schematic diagram. Figure 1 Take 10 mL of 10 vol% modified silicon carbide slurry prepared from the modified silicon carbide powder of Examples 1 to 4 and add it to a 10 mL colorimetric tube. 0 To measure the height of the modified silicon carbide slurry in the colorimetric tube before use, h is the height of the supernatant after settling for a period of time at room temperature. The smaller h is, the slower the silicon carbide particles settle in water and the better the stability.

[0078] After 48h sedimentation experiment of the modified silicon carbide slurry of Example 1, h / h 0 is 0.005, no obvious sedimentation; after 48h sedimentation experiment of modified silicon carbide slurry in Example 2, h / h 0 is 0.005, no obvious sedimentation; after 48h sedimentation experiment of modified silicon carbide slurry in Example 3, h / h 0 is 0.01, no obvious sedimentation; after 48h sedimentation experiment of modified silicon carbide slurry of Example 4, h / h 0 It is 0.01, and there is no obvious settlement.

[0079] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A modified silicon carbide slurry, comprising modified silicon carbide powder and water; the solid content of the modified silicon carbide slurry is 50-55 vol%; the viscosity is <1 Pa·s; The modified silicon carbide powder comprises silicon carbide and an ester modified layer and sodium humate sequentially coated on the surface of the silicon carbide; The method for preparing the modified silicon carbide powder comprises the following steps: The silicon carbide powder is acid-washed to obtain pure silicon carbide powder; The pure silicon carbide powder is mixed with an alkali solution and activated to obtain activated silicon carbide powder; The activated silicon carbide powder and a small molecule organic acid are mixed to perform a hydrothermal reaction, and the obtained powder is washed with a sodium humate solution to obtain a modified silicon carbide powder; The pickling method comprises: immersing silicon carbide powder in a hydrochloric acid solution; The mass fraction of the hydrochloric acid solution is 4 to 8%; The mass fraction of the alkali solution is 1.0 to 10.0%; the temperature of the activation treatment is 80 to 120° C.; the time of the activation treatment is 0.5 to 2 hours; The small molecule organic acid includes propionic acid, butyric acid or isobutyric acid; The mass ratio of the activated silicon carbide powder to the small molecule organic acid is 1-2:1-2.

2. The modified silicon carbide slurry according to claim 1, characterized in that: In the method for preparing the modified silicon carbide powder, the alkali solution includes sodium hydroxide solution, potassium hydroxide solution or sodium carbonate solution.

3. The modified silicon carbide slurry according to claim 1, characterized in that: In the method for preparing the modified silicon carbide powder, the temperature of the hydrothermal reaction is 80 to 120° C.; the time of the hydrothermal reaction is 0.5 to 4.0 hours.

4. Use of the modified silicon carbide slurry according to any one of claims 1 to 3 in the preparation of silicon carbide ceramics.

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